1. Field of the Invention
This invention generally relates to semiconductor manufacturing equipment and, more particularly, to an apparatus and method used for rapid thermal processing of a single semiconductor wafer.
2. Description of the Related Art
The advances in fabrication processes, especially of semiconductor devices of decreased dimensions, have necessitated the development of new processing and manufacturing techniques. One such processing technique is know as Rapid Thermal Processing (RTP), which reduces the amount of time that a semiconductor device is exposed to high temperatures during processing. The RTP technique, typically includes irradiating the semiconductor device or wafer with sufficient power to quickly raise the temperature of the wafer and hold it at that temperature for a time long enough to successfully perform a fabrication process, but which avoids such problems as unwanted dopant diffusion that would otherwise occur at the high processing temperatures. Generally, RTP uses a light source and reflectors to heat the wafer. In a conventional rapid thermal processor a lamp is used as the light source because of its low thermal mass, which makes it easy to power up and down very quickly.
Unfortunately, conventional lamp-based RTP systems have considerable drawbacks with regard to uniform temperature distribution. Any single variation in the power output from the lamps can adversely affect the temperature distribution across the wafer. Because most lamp-based systems use lamps with filaments, the wafer is usually rotated to ensure that the temperature non-uniformity due to the filament array is not transferred to the wafer during exposure. The moving parts required to rotate the wafer, adds to the cost and complexity of the system. Another particularly troublesome area for maintaining uniform temperature distribution is at the outer edges of the wafer. Most conventional RTP systems have no adequate means to adjust for this type of temperature non-uniformity. As a result, transient temperature fluctuations occur which may cause the formation of slip dislocations in the wafer at high temperatures (e.g.xcx9c1000xc2x0 C.).
Conventional lamp-based RTP systems have other drawbacks. For example, there are no adequate means for providing uniform power distribution and temperature uniformity during transient periods, such as when the lamps are powered on and off. Repeatability of performance is also usually a drawback of lamp-based systems, since each lamp tends to perform differently as it ages. Replacing lamps can also be costly and time consuming, especially when one considers that a given lamp system may have upwards of 180 lamps. The power requirement may also be costly, since the lamps may have a peak power consumption of about 250 kWatts.
For the above reasons, what is needed is an apparatus and method for isothermally distributing a temperature across the surface of a semiconductor device during rapid thermal processing.
The present invention provides a heating apparatus for isothermally distributing a temperature across a semiconductor device or wafer during processing. The invention includes an RTP chamber configured to receive a single semiconductor wafer. Housed within the chamber is a heating member or heating plate. Disposed on a periphery of the heating member is a heat source. Heat energy radiating from the heat source conducts through the heating member to create an isothermal temperature distribution across the heating member. Wafer supports are included on the heating member which support the wafer in close proximity to the heating plate, such that the temperature of the heating plate establishes the temperature of the wafer. Advantageously, this configuration permits the temperature to be uniformly and isothermally distributed over the wafer since the temperature distribution over the heating member is easier to achieve and maintain. The heating member may have a larger dimension than the outer dimension of the wafer, to ensure that the uniform temperature distribution at the outer edge of the wafer is maintained isothermal. Alternatively, a plurality of heating members may be stacked together within the process chamber. In this manner, the heating plates may be positioned above and below the wafer, such that the temperature of both heating plates influences the temperature distribution across the wafer.
In one aspect of the present invention, an apparatus is provided for heating a wafer during processing. The apparatus includes a process chamber, which defines a cavity. Disposed within the cavity is a heatable plate, which is configured to receive a wafer thereon. A heat source is disposed at a periphery of the heatable plate for creating a uniform temperature distribution across the heatable plate.
In another aspect of the present invention, a reactor is provided for rapidly and uniformly annealing a semiconductor wafer. The reactor includes a chamber, which defines a cavity. Disposed in the cavity is a conductive heating member. The heating member is configured to receive a wafer thereon. The reactor also includes a plurality of resistive heating elements positioned proximate to the chamber. A thermal energy output from each of the resistive heating elements provides a substantially isothermal temperature in the cavity.
The present invention overcomes the disadvantages of a lamp-based heating system since the heating member can provide a more uniform temperature distribution, for less power and reduced cost. The heating member can also conduct heat at a faster rate than the wafer, so that the wafer can more quickly arrive at the uniform temperature. No moving parts, such as lift pins or wafer spinners, are required within the cavity to load the wafer, nor are other complex and costly components, such as reflectors, actuators, and complex power transformers and controllers. Since the invention does not require large lamps for heating nor moving parts, the size of the chamber, as well as the volume of the cavity, may be substantially reduced relative to other chambers. The reduced volume and size are of particular advantage for reasons that are made apparent below.
These and other features and advantages of the present invention will be more readily apparent from the detailed description of the preferred embodiments set forth below taken in conjunction with the accompanying drawings.